In a small saucepan, whisk the eggs and sugar together until completely combined.

Whisk in the key lime juice, key lime zest, and salt.

Cook the mixture on low to medium heat, stirring constantly until the mixture is fully warm, about 5 minutes

Add the butter, one tablespoon at a time, until the butter is melted and the mixture is smooth.

Continue cooking and continuously stirring until the mixture is thick, creamy and coats the back of the spoon, about 8-10 minutes.

Remove the curd from the heat. You can strain the curd, if you like, but we like to leave it as is in our house.

Pour the key lime curd into a medium bowl, cover, and chill for about an hour.

Preheat the oven to 350ºF. Prep a 9 x 9 baking pan by generously spraying with cooking spray.

Using the paddle attachment of a stand mixer, cream the softened butter, sugar, baking soda, and salt together on high speed until light and fluffy, about 5 minutes. Be sure to scrape down the sides and bottom of the mixing bowl halfway through mixing to prevent any lumps from forming.

Reduce the mixer to slow speed and add the egg yolks one at a time, mixing well after each addition, followed by the vanilla.

Alternatively the cake flour and milk by adding one third of the cake flour, followed by one third of the milk. Mix each addition until it is roughly incorporated before adding the next. Be careful not to over mix the batter.

Pour the cake batter into the prepared cake pan. Bake at 350ºF for 25 minutes until the top is golden brown and a toothpick inserted into the center comes out clean, or it reaches 210ºF.

Once the cake has cooled for about 5 minutes, poke holes evenly across the cake for the filling.

While the cake is baking, get started on the Cinnamon Graham Cracker Crumble by adding the crushed graham crackers, sugar, and salt into a large mixing bowl. Mix until all of the ingredients are evenly dispersed.

Add the melted butter and vanilla and mix until all of the crumbs are evenly coated.

Evenly pour the mixture on to a quarter sheet pan with parchment paper on the bottom.

Once the cake is out of the oven, bake the crumble at 350ºF for 8 minutes, until the crumbs get crispy.

Remove from the oven and allow the crumbs to cool before breaking up into small chunks and crumbs for the topping.

Once the key lime curd has chilled for an hour, get started on your whipped key lime cream. In a stand mixer with the whip attachment, whip the heavy whipping cream, powdered sugar, and vanilla together on medium speed for 2 minutes.

Add 1 ½ cups of the key lime curd to the whipped cream and continue mixing on medium speed for 3 minutes, or until soft peaks begin to form.

Pour the remaining key lime curd over the holes poked into the cake. Be sure to allow the curd to fill each hole before pouring over the next one.

Spread the whipped key lime curd over the layer of curd.

Generously sprinkle with cinnamon graham cracker crumble.

Chill the cake in the fridge for an hour or so before cutting into it, to allow the topping time to set a little.